The present invention generally relates to the field of heterogeneous, wireless ad-hoc networks suitable for low-power, short-range and ubiquitous ad-hoc communication for fixed, embedded or portable devices, e.g. a wireless sensor network (WSN) for use e.g. in health care, intelligent household, industry, distributed computing or related applications.
A wireless ad-hoc communication network is typically based on ad-hoc multi-hop communications. The typical mode of communication in a sensor network is from multiple data sources to a data sink. During the lifetime of the network, the information collected by the sensors is periodically transmitted to the sink nodes, which can either be mobile or fixed. These sink nodes can be used by external operators to retrieve the information gathered by the network (gateway functionality). In addition, the wireless communication network enables communication and information exchange between any of the nodes participating in the network.
Since the data being collected by multiple sensors is often based on common phenomena, there is likely to be some redundancy in the raw or pre-processed data being communicated by the various nodes in sensor networks. Third, in most envisioned scenarios the sensors are not mobile (though the sensed phenomena may be), so the nature of the dynamics in both network types is different.
The single major resource constraint is that of energy for a small, embedded node hosting sensing and communication functions. The scale of sensor networks and the necessity of unattended operation for months at a time means that energy resources have to be managed even more carefully. This, in turn, typically precludes high data rate communication, long range wireless communication and any other type of complex data pre-processing
Current systems typically employ conventional low-power radio technology or Bluetooth radio systems, which require a substantial amount of energy for transmission and reception. Therefore, even if the traffic pattern is very sporadic, both units (receiver and transmitter) are turned on from time to time, need to be synchronized and finally exchange information (if there is any information to be exchanged). Typically for short-range wireless devices, the reception unit takes the same power (or even higher power) as the transmission unit. Even if no information needs to be received, substantial power is wasted just to be able to receive data. In order to save as much power as possible, complex duty-cycle radio protocols are employed. Duty cycling raises another problem: Information can only be exchanged during ‘on’ time, where both the transmitter and the corresponding receiver are activated at the same instance of time. Therefore, in a typical duty-cycle protocol—e.g. with a 1% duty cycle, which means that e.g. a transceiver is switched on for 0.1 seconds and turned off for 9.9 seconds—messages may need to be delayed substantially.
Said low-power radio technology and said Bluetooth radio systems are typically employed for each type of node within a wireless sensor network. Therefore, even the simplest nodes (and those may be deployed massively) use the same kind of radio technology (which consumes substantial power and imposes a certain system cost). A more suitable wireless network system would allow scaling of the radio subsystem and the radio protocol according to the respective node's task. At least the scaling of the radio protocol and routing protocol is partially used in current systems (e.g. by defining end points, routers and gateways).
A suitable radio technology for certain nodes in a wireless network for wireless sensor applications can be “Modulated Backscatter” (MBS), which is currently used for short-range radio frequency identification (RFID) applications (e.g. smart card access control systems). As there is no need for a complicated radio (passive transmission), both the cost and energy consumption can be very low (for many nodes within a wireless network). However, current MBS applications are limited to RFID style operation and therefore do not support the following points:                Efficient networking: Currently, a single “reader” talks to a group of RFID tags, information is not provided within a network and “tag-to-tag” communication is not supported.        Only a fixed, pre-programmed ID is provided by the tag, which means that there is no dynamic information generated, processed and communicated from the tag.        MBS range and data rate are limited due to the limited application scenario of RFID and the technology implemented.        Interworking (both on radio and radio protocol) with other “longer-range” radio technologies (e.g. ISM band short-range radio systems such as Bluetooth). Thereby, sensor information can not be propagated across different radio technologies. In addition, both radio technologies have been designed with different scenarios in mind and are thus not compatible.        